The present invention relates to a developer for electrophotography which is composed of a domain resin containing specified additives and being dispersed in a matrix resin containing a specified additives. The present invention relates also to a method for producing the same. The present invention also relates to a developing method using the developer.
There is known a developer of two-component type and single component type. The two component type is composed of a toner and a carrier, The single component type is composed of a toner. The present invention includes both types of the developer.
With respect to a toner for electrophotography, there have been generally known the ones which are prepared by the steps of melting and kneading a matrix resin as a binder, a coloring agent, a charge controlling agent and, if necessary, magnetic particles, pulverizing the kneaded material, and classifying the pulverized material to give a uniform specified particle size distribution.
The charge controlling agent is contained in the toner particles and distributed irregularly on the surface of the toner when the toner is prepared by the method of pulverizing as noted above. As a frictional electrification amount of toner depends on the conditions of the toner surface, the charge controlling agent inside the toner particle can not work effectively. Therefore, almost all the added charge controlling agent is useless.
In order to avoid the problem mentioned above, a charge controlling agent is made to exist on the surface or near the surface of the toner. The charge controlling agent is adhered to the surface by means of mechanical impact or chemical adhesion after toner particles are prepared. In this technique, when toner particles are nearly spherical, the charge controlling agent may be adhered to the surface uniformly to a certain degree. When toner particles are irregular, the charge controlling agent can not be adhered uniformly to concave portions and convex portions. Therefore, the distribution and adhesion of the charge controlling agent are not uniform. There arise such problems as separation of the charge controlling agent and non-uniformity of electrification amount. Moreover, as a charge controlling agent is expensive, it is important not to waste the agent.
A toner may contain magnetic particles in order to avoid toner scattering or to form a mono-component magnetic toner. However, when magnetic toner particles are prepared conventionally by a kneading and pulverizing method, the dispersion of magnetic particles is not uniform and the magnetic particles are exposed on the surface of the toner. The non-uniform dispersion and the exposure of the magnetic particles influence adversely. Toner particles are poorly charged. Such poorly charged toner particles are liable to be scattered and cause toner fogs and pollution inside a copying machine. Further, as magnetic particles are liable to be influenced by moisture, the environmental resistance becomes poor and the lowering of electrification amount of toner is caused. Moreover, magnetic particles exposed from the surface may injure a photosensitive member when electrostatic latent images are developed. The problems mentioned above become more remarkable as the magnetic particles are contained more.
With respect to a two component developer composed of a toner and a carrier, there is known a carrier of binder type in which carrier cores are dispersed in an adequate binder resin in order to improve environmental stability, prevention from abrasion or damages of a photosensitive member. Such a conventional binder-type carrier is generally black or gray. When the carrier particles are adhered to copying paper, the quality of copy images are deteriorated.